I. Field
The present disclosure relates generally to communication, and more specifically to techniques for sending feedback information in a wireless communication system.
II. Background
In a wireless communication system, a transmitter may utilize multiple (T) transmit antennas for data transmission to a receiver equipped with multiple (R) receive antennas. The multiple transmit and receive antennas form a multiple-input multiple-output (MIMO) channel that may be used to increase throughput and/or improve reliability. For example, the transmitter may transmit up to T data streams simultaneously from the T transmit antennas to improve throughput. Alternatively, the transmitter may transmit a single data stream from all T transmit antennas to improve reception by the receiver. Each data stream may carry one transport block or packet of data in a given transmission time interval (TTI). Hence, the terms “data stream” and “transport block” may be used interchangeably.
Good performance (e.g., high throughput) may be achieved by precoding one or more data streams with a precoding matrix selected based on the response of the MIMO channel from the transmitter to the receiver. Precoding may also be referred to as beamforming, spatial mapping, etc. The receiver may evaluate different possible precoding matrices and select a precoding matrix as well as the number of data streams to send such that the best performance can be achieved. The receiver may also determine a signal-to-interference-and-noise ratio (SINR) for each possible data stream and select a data rate for the data stream based on the SINR. The receiver may send feedback information that may include the selected precoding matrix, the data rate for each data stream, etc. The transmitter may process one or more data streams in accordance with the feedback information and send the data stream(s) to the receiver.
The feedback information may improve data transmission performance. However, valuable radio resources are consumed to send the feedback information. There is therefore a need in the art for techniques to efficiently send the feedback information.